[PATCH AUTOSEL 4.14 103/105] gtp: fix use-after-free in gtp_encap_destroy()

Sasha Levin
2019-07-15T14:35:40Z

From: Taehee Yoo <ap420073@gmail.com>

[ Upstream commit 1788b8569f5de27da09087fa3f6580d2aa04cc75 ]

gtp_encap_destroy() is called twice.
1. When interface is deleted.
2. When udp socket is destroyed.
either gtp->sk0 or gtp->sk1u could be freed by sock_put() in
gtp_encap_destroy(). so, when gtp_encap_destroy() is called again,
it would uses freed sk pointer.

patch makes gtp_encap_destroy() to set either gtp->sk0 or gtp->sk1u to
null. in addition, both gtp->sk0 and gtp->sk1u pointer are protected
by rtnl_lock. so, rtnl_lock() is added.

Test command:
gtp-link add gtp1 &
killall gtp-link
ip link del gtp1

Splat looks like:
[ 83.182767] BUG: KASAN: use-after-free in __lock_acquire+0x3a20/0x46a0
[ 83.184128] Read of size 8 at addr ffff8880cc7d5360 by task ip/1008
[ 83.185567] CPU: 1 PID: 1008 Comm: ip Not tainted 5.2.0-rc6+ #50
[ 83.188469] Call Trace:
[ ... ]
[ 83.200126] lock_acquire+0x141/0x380
[ 83.200575] ? lock_sock_nested+0x3a/0xf0
[ 83.201069] _raw_spin_lock_bh+0x38/0x70
[ 83.201551] ? lock_sock_nested+0x3a/0xf0
[ 83.202044] lock_sock_nested+0x3a/0xf0
[ 83.202520] gtp_encap_destroy+0x18/0xe0 [gtp]
[ 83.203065] gtp_encap_disable.isra.14+0x13/0x50 [gtp]
[ 83.203687] gtp_dellink+0x56/0x170 [gtp]
[ 83.204190] rtnl_delete_link+0xb4/0x100
[ ... ]
[ 83.236513] Allocated by task 976:
[ 83.236925] save_stack+0x19/0x80
[ 83.237332] __kasan_kmalloc.constprop.3+0xa0/0xd0
[ 83.237894] kmem_cache_alloc+0xd8/0x280
[ 83.238360] sk_prot_alloc.isra.42+0x50/0x200
[ 83.238874] sk_alloc+0x32/0x940
[ 83.239264] inet_create+0x283/0xc20
[ 83.239684] __sock_create+0x2dd/0x540
[ 83.240136] __sys_socket+0xca/0x1a0
[ 83.240550] __x64_sys_socket+0x6f/0xb0
[ 83.240998] do_syscall_64+0x9c/0x450
[ 83.241466] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 83.242061]
[ 83.242249] Freed by task 0:
[ 83.242616] save_stack+0x19/0x80
[ 83.243013] __kasan_slab_free+0x111/0x150
[ 83.243498] kmem_cache_free+0x89/0x250
[ 83.244444] __sk_destruct+0x38f/0x5a0
[ 83.245366] rcu_core+0x7e9/0x1c20
[ 83.245766] __do_softirq+0x213/0x8fa

Fixes: 1e3a3abd8b28 ("gtp: make GTP sockets in gtp_newlink optional")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/gtp.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index c751f87c935e..53fd66534e3a 100644
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -289,13 +289,17 @@ static int gtp1u_udp_encap_recv(struct gtp_dev *gtp, struct sk_buff *skb)
return gtp_rx(pctx, skb, hdrlen, gtp->role);
}

-static void gtp_encap_destroy(struct sock *sk)
+static void __gtp_encap_destroy(struct sock *sk)
{
struct gtp_dev *gtp;

lock_sock(sk);
gtp = sk->sk_user_data;
if (gtp) {
+ if (gtp->sk0 == sk)
+ gtp->sk0 = NULL;
+ else
+ gtp->sk1u = NULL;
udp_sk(sk)->encap_type = 0;
rcu_assign_sk_user_data(sk, NULL);
sock_put(sk);
@@ -303,12 +307,19 @@ static void gtp_encap_destroy(struct sock *sk)
release_sock(sk);
}

+static void gtp_encap_destroy(struct sock *sk)
+{
+ rtnl_lock();
+ __gtp_encap_destroy(sk);
+ rtnl_unlock();
+}
+
static void gtp_encap_disable_sock(struct sock *sk)
{
if (!sk)
return;

- gtp_encap_destroy(sk);
+ __gtp_encap_destroy(sk);
}

static void gtp_encap_disable(struct gtp_dev *gtp)
@@ -1045,6 +1056,7 @@ static int gtp_genl_new_pdp(struct sk_buff *skb, struct genl_info *info)
return -EINVAL;
}

+ rtnl_lock();
rcu_read_lock();

gtp = gtp_find_dev(sock_net(skb->sk), info->attrs);
@@ -1069,6 +1081,7 @@ static int gtp_genl_new_pdp(struct sk_buff *skb, struct genl_info *info)

out_unlock:
rcu_read_unlock();
+ rtnl_unlock();
return err;
}

--
2.20.1